Re: kern/48550: panic when accessing CDs

[David Laight <david%l8s.co.uk@localhost>]

The following reply was made to PR kern/48550; it has been noted by GNATS.

From: David Laight <david%l8s.co.uk@localhost>
To: gnats-bugs%NetBSD.org@localhost
Cc: 
Subject: Re: kern/48550: panic when accessing CDs
Date: Wed, 19 Mar 2014 19:00:59 +0000

 On Wed, Mar 19, 2014 at 03:45:00PM +0000, Martin Husemann wrote:
 ...
 >  As henning petersen pointed out in 48664, this is a side effect of gcc 4.8.
 >  Actually it turns out that the scsipi_read_cd_cap_data structure is
 >  misaligned on the stack (as it formally requires no alignement) by newer
 >  gcc and scsipi_command() doesn't seem to like this.
 >  
 >  This patch avoids that and makes the READ_CD_CAPACITY work:
 >  
 >  --8<--
 >  Index: scsipi_cd.h
 >  ===================================================================
 >  RCS file: /cvsroot/src/sys/dev/scsipi/scsipi_cd.h,v
 >  retrieving revision 1.21
 >  diff -u -r1.21 scsipi_cd.h
 >  --- scsipi_cd.h     1 Apr 2009 12:19:04 -0000       1.21
 >  +++ scsipi_cd.h     19 Mar 2014 15:35:33 -0000
 >  @@ -285,7 +285,7 @@
 >   struct scsipi_read_cd_cap_data {
 >      u_int8_t addr[4];
 >      u_int8_t length[4];
 >  -} __packed;
 >  +} __packed __aligned(4);
 
 ISTM that it might be worth removing the __packed and replacing
 the two fields with uint32_t - and then accessing with the correct
 endianness.
 
        David
 
 -- 
 David Laight: david%l8s.co.uk@localhost